1. Technical Field
The present exemplary embodiments relate to MRI (magnetic resonance imaging) which magnetically excites nuclear spin of an object with an RF (radio frequency) signal having the Larmor frequency and reconstructs an image based on NMR (nuclear magnetic resonance) signals generated due to the excitation. More particularly, the present exemplary embodiments relate to a magnetic resonance imaging apparatus and a magnetic resonance imaging method that can image CSF (cerebrospinal fluid).
2. Related Art
Magnetic Resonance Imaging (MRI) is an imaging method that excites nuclear spin of an object set in a static magnetic field with an RF signal having the Larmor frequency magnetically and reconstructs an image based on NMR signals generated due to the excitation.
In the field of the magnetic resonance imaging, MRA (magnetic resonance angiography) is known as a method of obtaining an image of a blood flow. An MRI without using a contrast medium is referred to as a non-contrast MRA. As the non-contrast enhanced MRA, an FBI (fresh blood imaging) method that performs an ECG (electrocardiogram) synchronization to capture a pumping blood flow is ejected from the heart, thereby satisfactorily representing a blood vessel.
In MRA, “labeling” (synonymous with tagging) is performed on blood in order to better depict a blood vessel. As a method of labeling blood, there is known a time spatial labeling inversion pulse (t-SLIP) method (for example, see Japanese Patent Laid-Open No. 2009-28525). According to the t-SLIP method, a specific blood vessel can be selectively depicted using a non-contrast MRA.
FIG. 1 is an explanatory drawing explaining a data acquisition method using a conventional t-SLIP method.
In FIG. 1, the abscissa axis indicates time. As illustrated in FIG. 1, according to the t-SLIP method, when a region selective inversion recovery (IR) pulse is applied as a labeling pulse, the blood in a labeling region is labeled. Then, when a BBTI (Black Blood Traveling Time) has elapsed since the region selective IR pulse is applied, imaging data acquisition is performed. Then, as illustrated in FIG. 1, in order to make dynamic observation on a blood flow, the BBTI is changed for each data acquisition before imaging is performed. For this reason, if a large number of different BBTIs with small difference are set, dynamic observation can be made on the blood flow corresponding to a more detailed change in time.
Further, in the t-SLIP method, a method of applying a plurality of labeling pulses has been devised.
FIG. 2 is a drawing explaining a data acquisition method with application of a plurality of labeling pulses using the conventional t-SLIP method.
In FIG. 2, the abscissa axis indicates time. As illustrated in FIG. 2, according to the t-SLIP method, a plurality of BBTIs can be set to one data acquisition by applying a plurality of labeling pulses at each different timing. In addition, the spatial position of applied labeling pulses can also be changed. By doing so, not only various blood vessels but also the CSF can be selectively depicted or suppressed.
However, the CSF has no periodicity such as a cardiac cycle and the CSF flow greatly changes for each data acquisition timing. In light of this, from images acquired by the t-SLIP method, it is possible to understand a dynamic behavior of a periodic fluid, but it is difficult to understand a dynamic behavior of a non-periodic fluid accurately.
Moreover, when a plurality of labeling pulses are applied, the periods from the application timing of the respective labeling pulse to data acquisition timing are changed respectively. For this reason, the method of applying a plurality of labeling pulses cannot generate images representing a dynamic fluid behavior of synchronous time.
Furthermore, the CSF is greatly different in flow depending on its position. In light of this, the t-SLIP method of performing data acquisition a plurality of times by changing the BBTI has difficulty in following and imaging the CSF whose flow is changed. Moreover, in order to understand the CSF flow at a plurality of positions using the t-SLIP method, imaging needs to be performed at a different timing for each position. For this reason, the t-SLIP method cannot allow a wide range of CSF flow of synchronous time to be understood.
In addition, in the t-SLIP method, contrast is greatly changed due to a change in the period from the application timing of the labeling pulse to the data acquisition timing. For this reason, in the t-SLIP method, it is very difficult to visually understand a detailed dynamic CSF behavior from monochrome image in grayscale.